1. Field of the Invention
The present invention relates to data and metadata management in a hierarchical data storage system and more particularly to management of metadata in the form of tables of contents (TOC), each describing an aggregation of data objects, and aggregated sets of tables of contents (TOC Set).
2. Description of Related Art
Conventionally, a data storage management application stores individual data objects, such as files and directories, in a storage hierarchy linked to the storage management server. The storage hierarchy typically includes one or more levels of data storage media that correspond to the accessibility of the stored data. For example, one level may include a number of direct access storage devices (DASD's) that provide relatively fast access to stored data. Another level may include a plurality of sequential access storage devices that provide slower access to data, but typically are more cost effective as measured by the data storage capacity per storage device cost.
The current method of storing individual data objects in a storage hierarchy provides a high degree of management granularity, but requires substantial storage and storage management overhead. In other words, each of the data objects can be accessed, retrieved, moved, or otherwise manipulated independent of all other data objects. The price for management at this level can be significant in that a storage management server must maintain a database tracking each of the individual data objects. Thus, the storage management server database may require a prohibitive storage capacity in order to store all of the metadata associated with all of the data objects. Additionally, the overall operation complexity may be considerably greater in order to provide the management granularity.
Another approach in managing data objects within a storage hierarchy employs composite objects that contain multiple data objects aggregated into a single operable storage object. For example, one composite object may contain all of the data objects in an entire file system. A backup of the file system, instead of creating numerous data objects and corresponding metadata entries in the database, may be fully contained in a single composite object for which only one database entry is required in the storage management server database.
Such a composite object, whether created for backup purposes or other storage management purposes, is commonly referred to as an image. The backup image created in this scenario described contains all of the data objects from the file system and may be stored as a single object in the storage hierarchy, such as on magnetic tape.
The use of images in a storage hierarchy may greatly reduce the management complexity in that the storage manager server may manipulate all of the data objects in a single image as a single object. Storing the data objects as a single image may also enable more rapid backup and restore operations on the data within the image.
Current hierarchical data storage systems, however, do not provide for improved management of the metadata associated with the data objects in an image. It would be a great advantage in the art to provide a process and apparatus capable of reducing the overhead required to manage such metadata in a manner similar to the management of the data objects in an image.